Field of the Invention
The invention pertains to the field of tensioners. More particularly, the invention pertains to a tensioner with spring force control in a second bore of the housing.
Description of Related Art
Generally, in timing chains for valve drives of internal combustion engines, camshaft chains in use for a camshaft-camshaft drive, and balancer chains have tensioners that are used on the slack side of a chain to take up slack in the chain and to apply tension to the chain.
During operation, a piston of the tensioner presses against the chain to maintain tension in the chain. When tension in the chain increases during operation due to resonance of a chain span, a high load from the chain acts on the piston of the tensioner, causing the piston to extend as the tensioner pumps up to keep the tension in the chain.
Chain drive tensioner spring force is often too high for most operating conditions because the spring force needs to be sufficient to handle worst case operating conditions of the tensioner system. The effectiveness of the tensioner and the overall system behavior and efficiency could be improved if the tensioner spring force could be varied with operating conditions, taking into account wear and stretching that occurs in the chain during the life of the chain.